NOISE AND VIBRATION CONTROL Episode 4 pptx

TM 5-805-4/AFJMAN 32-1090 Table 4-6. Transmission Loss (in dB) of Stud-Type Partitions. (Cont’d) Improvement A. 1. These values may be added to TL of Type 1 or Type 3 partition if l/2-in. thick fibrous "sound-deadening board" is installed between studs and each layer of gypsum board. 2. These values may be added to TL of each type partition if resilient spring clips or resilient metal channels are used to support one layer of gypsum board on one side of the set of studs. (For Type 2, delete the second layer of gypsum board on this side; keep two layers on opposite side.) No significant additional benefit will result from combining resilient supports and sound-deadening board under the same layer of gypsum board. Improvement B. 1. If full area 3-in. thick glass fiber or mineral wool is loosely sup- ported inside the air cavity between walls, add these values to TL of Type 1 or Type 2 partition. Acoustic absorption material must not contact both interior surfaces of gypsum board (i.e., must not serve as partial "sound bridge" between walls). 2. If minimum l-l/2-in. thick glass fiber or mineral wool is loosely supported inside the air cavity, add these values to TL of Type 3 parti- tion or add one half these values to TL of Type 1 or 2 partition. Follow precautions of Step B.l above. Regarding both Improvements A and B. The combined TL benefits of one type A improvement and one type B improve- ment can be applied to each of the partition types shown. More than two of these improvements to one partition will result in no significant additional TL benefit. for the Type 3 acoustical material must be 0.65. The estimated TL of a Type 3 floor-ceiling is given in table 4-14 for a few typical dimensions of concrete floor slab thickness and air space. (4) Type 4 floor-ceiling. This floor-ceiling com- bination consists of a concrete floor slab, an air space, and a resiliently supported plaster or gyp. bd. ceiling. This combination is for use in critical situations where a high TL is required. The ceiling should have a minimum 12 lb/ft.2 surface weight and the plemum space should be at least 18 inches high. The estimated TL of the Type 4 floor-ceiling combination is given in table 4-15 for a few typical dimensions of floor slab, air space, and ceiling thicknesses. (a) Resiliently supported ceiling. The ceiling should be supported on resilient ceiling hangers that provide at least 1/10 inch static deflection under load. Neoprene-in-shear or compressed glass fiber hangers can be used, or steel springs can be used if they include a pad or disc of neoprene or glass fiber in the mount. A thick felt pad hanger arrangement can be used if it meets the static 4-12 deflection requirement. The hanger system must not have metal-to-metal short-circuit paths around the isolation material of the hanger. Where the ceiling meets the vertical wall surface, the perime- ter edge of the ceiling must not make rigid contact with the wall member. A 1/4-inch open joint should be provided at this edge, which is tilled with a nonhardening caulking or mastic or fibrous packing after the ceiling plaster is set. (b) Critical locations. Critical locations re- quire special care, Caution: This combination should be used only in critical situations, and special care must be exercised to achieve the desired TL values: full vague floor weight and thickness, no holes through the floor, and com- pletely resiliently supported nonporous dense ceil- ing. If the plaster of gyp. bd. ceiling is not supported resiliently, the TL value will fall about midway between the Type 3 and Type 4 values for the corresponding dimensions and floor slab weights. (5) Type 5 floor-ceiling. The “floating concrete floor”, as shown on figure 4-4, is a variation that TM 5-805-4/AFJMAN 32-1090 Table 4-7. Transmission Loss (in dB) of Plywood, Lumber, and Simple Wood Doors. Octave Frequency Band (Hz) 31 63 125 250 500 1000 2000 4000 8000 Thickness of Plywood or Lumber (in.) 1/4 1/2 1 2 4 Approximate Surface Weight (lb/ft. 2 ) 1 2 4 8 16 0 2 7 12 17 2 7 12 17 18 7 12 17 18 19 12 17 18 19 22 17 18 19 22 30 18 19 22 30 35 19 22 30 35 39 22 30 35 39 43 30 35 39 43 47 STC 18 21 24 28 33 Notes: 1. Surface weight based on 48 lb/ft. 3 density, or 4 lb/ft. 2 per in. thickness. 2. Lumber construction requires tongue-and-groove Joints, overlapping joints, or sealing of joints against air leakage. For intermediate thicknesses, interpolate between thicknesses given in table. 3. For ungasketed hollow-core flush-mounted wood doors, use TL for l/h-in. thick plywood. 4. For solid-core wood doors or approximately 2-in. thickness, well gasketed all around, use TL for 2-in. thick plywood. 5. For small-area doors or boxes, framing around Cage of panel adds effec- tive mass and stiffness and will probably give higher TL values than shown. can be added to any one of the Type 1 through 4 (a) Support of floating floor. The floating combinations. This becomes necessary when all concrete floor should be supported off the structure other floor systems clearly fail to meet the floor at a height of at least 2 inches with properly required TL values. The values given in table spaced blocks of compressed glass fiber or multiple 4-16 are improvements in TL that can be added layers of ribbed or waffle-pattern neoprene pads or to the values of tables 4-12 through 4-15 if a steel springs in series with two layers of ribbed or well-designed and well-constructed floating floor waffle-pattern neoprene pads. The density and is used. Where careful designs have included loading of the compressed glass fiber or neoprene prevention of flanking paths of sound or vibra- pads should follow the manufacturers’ recommen- tion, the table 4-16 values have been achieved dations. If steel springs are used, their static and even exceeded. However, if flanking paths deflection should not be less than 1/4 inch. In some are not prevented by intentional design consider- systems the 2-inch space between the floating slab ations, only one-half of these improvements may and the structure slab is partially filled with a be reached. 1-inch thickness of low-cost glass fiber or mineral 4-13 TM 5-805-4/AFJMAN 32-1090 Table 4-8. Transmission LASS (in dB) of Glass Walls or Windows. Octave Frequency Band (Hz) 31 63 125 250 500 1000 2000 4000 8000 STC Thickness of Glass (in.) 1/8 1/4 1/2 3/4 Approximate Surface Weight (lb/ft 2 ) 1-1/2 3 6-1/2 10 2 7 13 17 8 14 19 22 13 20 24 26 19 25 27 28 23 27 29 29 27 28 29 30 27 28 31 32 27 31 36 38 31 34 40 43 26 28 30 31 Notes : 1. Variations in surface area and edge-clamping conditions can alter the TL values considerably. There is not much consistency among published data. 2. TL tests usually are not carried out at 31-63 Hz; values given are estimates only. 3. In typical operable windows, poor seals can reduce these values. 4. Special laminated safety glass containing one or more viscoelastic layers sandwiched between glass panels will yield 5-10 dB higher values than given here for single thicknesses of glass; available in approxi- mately 1/4- to 3/4-in. thicknesses. wool blanket of 3- to 4-lb/cu feet density. Around all the perimeter edges of the floating floor (at the walls and around all concrete inertia bases within the floating floor area), there should be l-inch gaps that should later be packed with mastic or fibrous filling and then sealed with a waterproof nonhar- dening caulking or sealing material. A curb should be provided around the perimeter of the floated slab to prevent water leakage into the sealed perimeter joints, and several floor drains should be set in the structure slab under the floating slab to provide run-off of any water leakage into this cavity space. (b) Area of floating slab. The floating slab should extend over the full area that needs the added protection between the noisy and the quiet 4-14 spaces. The floating floor should not support any large, heavy operating equipment. Instead, such equipment should be based on extra-height house- keeping pads that protrude above the floating floor. The floating floor is beneficial, however, in reducing transmitted noise from lightweight equip- ment and pipe and duct supports. Figure 4-5 offers suggestions on applications and details of floating floors. (c) Prevention of flanking paths. Figure 4-6 illustrates possible flanking paths (paths 2 and 3) of noise and vibration caused by airborne excita- tion of walls and columns in the mechanical equipment room. These paths make it impossible to achieve the low noise levels that the floating floor and resilient ceiling would permit (via path TM 5-805-4/AFJMAN 32-1090 Table 4-9. Transmission Loss (in dB) of Typical Double-Glass Windows, Using 1/4-in Thick Glass Panels With Different Air Space Widths. Octave Frequency Width of Air Space (in.) Band (Hz) 1/4 1-1/2 6 31 13 14 15 63 18 19 22 125 23 26 30 250 26 30 35 500 29 34 40 1000 34 38 43 2000 31 37 44 4000 34 41 50 8000 38 46 54 STC 31 37 43 Notes : 1. For maximum acoustic performance, each sheet of glass should be mounted in soft sealing gaskets to minimize rigid , structural connections between the sheets. 2. See notes under Table 5-14. 1). Airborne excitation of structural surfaces in the mechanical equipment room should be prevented by protecting all walls and columns with isolated second walls or encasements. As an alternative, the radiating walls and columns in the quiet receiving room can be covered with isolated second walls or encasements. (6) Nonflat floor slabs. The above five types of floors are assumed to be of flat slab construction. Other popular forms are of a beam-slab type that provides stiffening beams combined with thin sec- tions of concrete, such as prestressed cored slabs, T-shaped beams, and coffered pan construction (fig 4-7). Since the thin section usually accounts for about 60 to 80 percent of the total floor area, the TL is largely influenced by the thickness and area of the thinnest section. The thick web of the beam component gives mass and stiffness, and this should improve the low-frequency TL. There is no collection of measured data on these types of floors, so only a rough estimating procedure is suggested. First, it is necessary to estimate the surface weight (in lb/ft.2) of the thinnest section of concrete and also to estimate the average surface weight of the total floor. Second, the arithmetic average of these two surface weights is obtained, and this average is used to enter tables 4-12 through 4-15 for the TL of the equivalent weight of a flat concrete slab. If the resulting average corresponds to a surface weight of less than 6-inch- thick solid concrete, the floor is not recommended for the support of large mechanical equipment directly above category 1 through 3 spaces (table 2-2). All floor slab recommendations given in the manual area are based on acoustical consider- ations and should not be construed as referring to the structural adequacy of the slabs. (7) Noise reduction (NR) of floor-ceilings. The procedure for determining the noise reduction of floor-ceiling construction is identical to that given in Section 4-2.b for walls. The area SW now becomes the floor area common to the source and receiving rooms, and the correction term C is now called the “floor correction term,” but it is still obtained from table 3-1. 4-15 TM 5-805-4/AFJMAN 32-1090 Table 4-10. Transmission Loss (in dB) of a Filled Metal Panel Partition and Several Commercially Available Acoustic Doors. Octave Filled Acoustic Doors, Nominal Thicknesses Frequency Metal Band Panel 2-in. 4-in. 6-in. 10-in. Two Sets 4-in. Doors (Hz) Partition a Thick b Thick C ThicK d Thick e in Double Walls 32-in. Air Space f 31 19 27 34 42 63 22 29 37 48 125 26 31 34 41 47 54 250 31 34 36 47 53 60 500 36 37 40 52 61 67 1000 43 39 45 55 66 75 2000 48 43 49 59 65 84 4000 50 47 51 62 69 90 8000 52 60 95 STC 41 40 45 58 64 71 Notes: a Constructed of two 18 ga. steel panels filled with 3 in. of 6-8 lb/ft. 3 glass fiber or mineral wool; Joints and edges sealed airtight. b Average of 4 doors, l-3/4- to 2-5/8-in. thick, gasketed. c Average of 2 doors, all 4-in. thick, gasketed around all edges, range of weight 12-23 lb/ft. d Average of 4 doors, 6- to 7-in. thick, gasketed, installed by manufacturer, range of weight 23-70 lb/ft. 2 e Average of 2 doors, each 10-in. thick, gasketed, installed by manufacturer, range of weight 35-38 lb/ft. 2 f Estimated performance, in isolated 12-in. thick concrete walls, no leakage, no flanking paths. 4-16 [...]...TM 5-805 -4/ AFJMAN 32-1090 Figure 4- 7 Nonflat Concrete Floors Figure 4- 6 Structureborne Flanking Paths of Noise (Paths 2 and 3) Limit the Low Sound Levels Otherwise Achievable with High-TL Floating Floor Construction (Path 1) 4- 22 TM 5-805 -4/ AFJMAN 32-1090 CHAPTER 5 SOUND PROPAGATION OUTDOORS 5-1 Introduction Mechanical equipment such as cooling towers, rooftop units and exhaust fans are... lengths “a” and “b”) At twice the distance, 2d, the lengths a and b are expanded to 2a and 2b, and the resulting area over which the sound is now spread has become 4A, 4 times the area back at distance d Sound pressure level is related to the “energy per unit area” in the sound wave; so, in traveling twice the original distance from the source, the energy per unit area has decreased by a factor of 4 which... negligible and are ignored in this simplifying table The table 5-3 values can be applied to all octave bands for most close-in situations However, at larger distances the absorption and attenuation effects become significant, and table 5 -4 gives the distance terms as a function of the octave bands for distances from 80 feet out to 8000 feet (2) SPL at another distance from known SPL Equation 5 .4 can be... - DT2 + DT1, (eq 5 -4) where Lp1 is the known SPL at distance d,, and Lp2 is the wanted SPL distance d2 The distance terms DT1 and DT2 are evaluated in equation 5-3 5-2 or obtained from tables 5-3 and 5 -4 This equation applies when d 1 is greater than the physical dimension of the sound source 5-3 Atmospheric Effects Wind and temperature variations can cause bending of sound waves and can influence changes... temperature and relative humidity of the octave frequency bands A “standard day” is frequently defined as having a temperature of 59 deg F and a relative humidity of 70 percent For long-time average sound propagation conditions, the molecular absorption coefficients for standard day conditions should be used For any specific application of measured or estimated SPL for known temperature and humidity... normally short-term effects and do not provide reliable noise control However, they help explain the variations that occur in outdoor sound propagation and measurements a Wind effects A steady, smooth flow of wind, equal at all altitudes, would have no noticeable effect on sound transmission In practice, however, wind speeds are slightly higher above the ground than at the ground, and the resulting wind... equipment outdoors Unacceptable noise from electrical or mechanical equipment, whether located indoors or outdoors, may be strong enough to be transmitted to neighbor locations The sound transmission paths are influenced by three broad types of natural effects: distance effects, atmospheric effects, and terrain and vegetation effects In addition, structures such as barriers and buildings influence the... rate of 6 dB for each doubling of distance from the source An equation and a table incorporating this effect are given in paragraph 5-2d b Molecular absorption In addition to the reduction due to the inverse square law, air absorbs sound energy, and that the amount of absorption is dependent on the temperature and humidity of the air and the frequency of the sound Table 5-1 gives the molecular absorption... energy by “molecular absorption,” and small amounts of ever-present air movement and inhomogeneities give rise to “anomalous excess attenuation.” These three distance effects are summarized in the following paragraphs a Effect of distance Figure 5-1 illustrates the “inverse square law” for drop-off of SPL with distance A point source of sound is shown at point “X”, and the rays show the path of an element... natural effects and structural interferences in outdoor sound propagation are given in this chapter 5-2 Distance Effects Acoustical energy from a source spreads out as it travels away from the source, and the sound pressure level drops off with distance according to the “inverse square law.” This effect is common to all types of energy propagation originating from an essentially point source and free of . 48 125 26 31 34 41 47 54 250 31 34 36 47 53 60 500 36 37 40 52 61 67 1000 43 39 45 55 66 75 2000 48 43 49 59 65 84 4000 50 47 51 62 69 90 8000 52 60 95 STC 41 40 45 58 64 71 Notes: a Constructed. (in.) (Hz) 1 1 1 14 2 31 33 38 41 44 16 63 39 42 44 46 48 125 41 43 46 48 51 250 44 48 51 54 58 500 50 54 57 60 64 1000 56 61 64 66 69 2000 61 66 70 72 74 4000 67 72 75 76 77 8000 70 75 78 81 83 STC 55 59 61 64 68 Note : 1. If. (in.) 4 6 8 10 12 Octave Frequency Band (Hz) 31 29 33 35 37 38 63 35 37 38 39 40 125 37 38 40 41 42 250 38 41 44 46 48 500 43 47 49 51 53 1000 48 53 54 56 57 2000 53 57 59 61 62 40 00 57 61 63 64 65 8000 61